Im having trouble with the FC. Over night test it will dip to 1 or even below. During the day it hovers around 2. But I can't get it any higher even when I have the SWG set on 80%. The pool water is blue but perhaps has a very slight haze especially during the morning before the pump comes on. But not enough to be called cloudy or change the color of the water.
I've cleaned the filter, cleaned the salt cell, added CYA (because that was a little low), and for the past two days the SWG has been on 80%. No dice...can't get the FC above 2.0.

CC is zero and phosphates are also zero. Salt is 3400. There is no evidence of algae growth. So im thinking either something is wrong with the cell or something in the pool has to be eating up the FC. pH is in range but alkalinity is a bit low but dont think that has anything to do with this.

Should I shock the pool? Have the SWG checked? Increase the pump run time and give the cell a few more days?

Thanks for any help.

Welcome to the forum!

take a sample just as it comes out of the return and test that for CL to prove that the SWG is working.

Once you have confirmed that, there are two things that consume chlorine....organics in your pool and UV from the sun. You can retard the UV loss with adequate CYA.....what is that test result.

If you have organics (algae) in your pool (which I suspect) you will need to shock. Report that CYA result and we can go from there.

FC from one of the returns is 2.8.
FC away from the return is 2.0.

CYA was in the 30s when I checked it late last week and I added a pound which has just recently fully desolved. So I doubt I will get a accurate test result right now. I'm planning to add another pound if it needs it in a week or so.

If your SWG is still at 80%, I think your FC at the return should be MUCH higher.

What size is your pool?

Did another test... At the return it's about 3.5. Away from the return it's now 2.4. About 2 hours since the previous test (and sun has been down since last test). Also it appears I might have a slight reaction of CC now at 0.2.

It's a pentair IC-20 on 80% and pool is about 10,000 gals.

It's been on for about 10 hours now so I would think it should have a higher FC.

If your CYA was 30 and you added 1 lb, you should be around 40+. I would add the other lb now and get it at least to 55-60.

Then, as a cheap first step, I would shock the pool according to the procedure taught in Pool School using liquid chlorine (clorox). Once the shock process is complete, see if your FC will then start to increase rather easily.

If it still doesn't, then I believe you have an output issue with the SWG.

What is the water temp?

I suggest running the overnight chlorine loss test again but with a higher chlorine amount to begin with. Put in a 182oz jug of 6% bleach at least an hour before you turn off the pump for the night. Take your chlorine reading that night and again before sun hits the pool. If you have more than 1ppm loss then you have organics in the water. This test will determine if you have organics or something else wrong with the cell.

If your water temp is too cold your cell will not function properly. That's why Butterfly wants to know the water temp.

I ran the system overnight to see how much chlorine is added. It went from 2.0 at dusk to near 4 at morning with CC at 0.5. Water had a slight aqua shade to it. At that point I added some bleach and got it up to 10. A check 8 hours later showed it 10.5 (with SWG at 60%) and CC has dropped to zero. Water has gotten bluer. Enough CYA has been added to bring it up to 80 although I can't test for that yet of course.

I'll do the overnight test tonight again. And then watch the levels closely over the coming days to see if the SWG is maintaining it.

Out of curiosity, what should be normal output on a SWG?

I know Pentair says the IC-20 for example will put out a max of 0.7 lbs per day. That would be only about a 1/2 ounce per hour @100% output if my math is right. I wouldnt think a measurement from the return would be very much higher with that...maybe 1 ppm? Also if there is algae in the pool, or low CYA, I wouldnt think that would be enough rise to keep up with demand. You would have to shock it or raise the FC from an outside source, right?

Just a hypothetical here...

You should shut the system off overnight and see how much is lost. THAT will be the telling factor.

OK, so Im still getting a FC loss at night consistantly of around 1.5. My CC seems to go from 0 to .5 to 0 at random. And I have that chlorine smell at times. It seems to maintain the correct level during the day and the water is blue.

Should I just try a full shock with bleach?

FC loss is caused by two things: Sunlight/UV and organic nasties in the water. If you are losing FC at night, then you have organics in the water which is consuming your chlorine as the chlorine attempts to remove it.
So you are correct in that you need to shock the pool with chlorine, and bleach is the best stuff to use. You should read through Shocking your pool in Pool School.

Time to go through the shock process sounds like!

By the way, phosphates do NOT matter.

Please read Pool School and learn the shock process, don't listen to the pool store when it comes to getting this right.

My pool was going through nearly the same process last spring, water looked clear, .5 CC, but was consuming FC overnight. I followed the shock process in pool school and passed the OCLT in 5 days. The water was more sparkly afterwards but without the OCLT I would have never guessed I had anything in the water. I have followed the Chlorine/CYA table in pool school since then, and have had no problems holding FC.

So its been a few weeks.

I brought the pool up to shock level and it seemed to eliminated whatever was causing the FC demand. The SWG is now easily maintaining the current level at around 8 with even the lowest setting (20%).

However for the last week my CC crept back up slightly from 0 after the shock to around 0.25 to 0.5. But again it doesnt appear to be affecting the FC at least right now. The SWG is easily holding it. Water has also completely cleared up and is crystal blue.

Should I be concerned about that CC or just keep an eye on it?

Overnight test also yields no more than .5 decrease in FC at most.

.5 cc's or less is just fine. for pool purposes, it's practically as good as zero. It is very common for most pools to have some cc's and is only troublesome when they climb to 1.0 or greater.

If you have a pool cover, then opening the pool to expose it to sunlight can help control CC though as Dave points out a CC of 0.5 or less is not a problem.

Congratulations on getting things stable again. I've been through that a few times. I'm starting to learn that if I see a sudden FC drop in the summer that it's just time to shock the pool. I've been tracking things in a spreadsheet and I seem to go through a few weeks of frustration and then realize I need to shock when things are a little worse (often nothing visible or cloudy yet). Still, if it's shocked when I first saw it, it would have taken care of the problem.

Your sig doesn't show what kind of filter you have. Now that you have things cleaned up, you might want to backwash/clean/whatever your filter. I have a DE filter and after one of those episodes, I see the pressure go up and need to backwash it.

I know a lot of people here oppose high cya, but a lot of salt water systems require about 60ppm cya!
Getting CAC every night suggests Organic/Inorganic waste. Usually a dirty/older filter media.
Did you know shocking with chlorine actually can increase inorganic waste?! if im not mistaken. There is an article by DuPont about non-chlorine shocks that everyone should read.